Research on Time Transfer Method Based on Un-Differenced Combination Model Between Stations

Time is an indispensable element in daily production and life, and accurate time information plays an irreplaceable role in basic scientific research and national defense construction. Taking advantage of GNSS measurement accuracy and wide coverage, long-distance time transfer can be performed. In view of the problems of high accuracy requirements for long-distance time transfer and the difficulty of accurately predicting satellite clock offset, we proposed a carrier phase time transfer method based on the un-differenced combination model between stations, which does not require high-precision satellite clock offset products and can complete time transfer only by using satellite orbit products. Based on the ultra-fast satellite orbit products provided by the International GNSS Service (IGS), the data from the IGS Observatory are used for time transfer experiments. The results showed that sub-nanosecond accuracy can be achieved by using this model in real-time long-distance time transfer, and the transfer accuracy and stability are better than the traditional PPP model, indicating that the model has good applicability and stability in long-distance time transfer.